Near-Perfect CO_2/CH_4 Selectivity Achieved through Reversible Guest Templating in the Flexible Metal-Organic Framework Co(bdp)

摘要

Metal–organic frameworks are among the most promising materials for industrial gas separations, including the removal of carbon dioxide from natural gas, although substantial improvements in adsorption selectivity are still sought. Herein, we use equilibrium adsorption experiments to demonstrate that the flexible metal–organic framework Co(bdp) (bdp~(2–) = 1,4-benzenedipyrazolate) exhibits a large CO_(2) adsorption capacity and approaches complete exclusion of CH_(4) under 50:50 mixtures of the two gases, leading to outstanding CO_(2)/CH_(4) selectivity under these conditions. In situ powder X-ray diffraction data indicate that this selectivity arises from reversible guest templating, in which the framework expands to form a CO_(2) clathrate and then collapses to the nontemplated phase upon desorption. Under an atmosphere dominated by CH_(4), Co(bdp) adsorbs minor amounts of CH_(4) along with CO_(2), highlighting the importance of studying all relevant pressure and composition ranges via multicomponent measurements when examining mixed-gas selectivity in structurally flexible materials. Altogether, these results show that Co(bdp) may be a promising CO_(2)/CH_(4) separation material and provide insights for the further study of flexible adsorbents for gas separations.